1. Field of the Invention
The invention relates to silicone compositions which comprise inactive fillers and nitrogen compounds which can be crosslinked to provide elastomers, and to the silicone elastomers obtainable therefrom.
2. Background Art
As is known, the oil resistance of silicone elastomers can be improved by addition of, for example, quartz or talc. U.S. Pat. No. 4,131,588 describes mica- and optionally talc-containing addition- and condensation-crosslinking silicone compositions having reduced gas permeability. European published application EP-A-953675 describes the use of talc as filler in textile coating compositions. The condensation- or addition-crosslinking silicone elastomers have reduced friction owing to the talc. These compositions are principally employed in airbag coating.
However, talc and other non-reinforcing fillers cause a considerable weight loss in silicone compositions or silicone elastomers at temperatures above 100xc2x0 C. It has been found, for example, that talc and quartz cleave the siloxane chain at elevated temperatures and thus catalyze the formation of cyclic, volatile siloxane compounds. This results in the heat stability of the silicone compositions and silicone elastomers being unsatisfactory at temperatures above 100xc2x0 C.
An object of the present invention was to provide silicone compositions and silicone elastomers which, despite being filled with non-reinforcing fillers, have improved heat stability. This and other objects are met by peroxidically crosslinkable or addition crosslinkable silicone compositions which can be crosslinked to form elastomers, these crosslinkable compositions containing both a non-reinforcing filler and a nitrogen-containing compound.
The invention thus relates more particularly to silicone compositions which can be crosslinked to give elastomers and which comprise the constituents
(A) from 20 to 99% by weight of a polyorganosiloxane containing at least two alkenyl groups per molecule and having a viscosity at 25xc2x0 C. of from 0.1 to 500,000 Pa.s,
(B) from 1 to 80% by weight of a non-reinforcing filler having a mean particle size of from 0.1 to 200 xcexcm and a specific surface area of  less than 100 m2/g,
(C) a crosslinking component selected from
(C1) an organic peroxide and
(C2) an organosilicon compound containing at least two SiH functions per molecule in combination with a hydrosilylation catalyst, and
(D) a nitrogen compound which is selected from amino, ammonium and amido compounds and nitrogen-containing organosilicon compounds.
The inventors have surprisingly discovered that the addition of amino or ammonium compounds to silicone compositions which can be crosslinked to give elastomers drastically reduces cyclization and thus weight loss at elevated temperatures and therefore enables more stable mechanical properties to be achieved on exposure to heat.
The composition of the polyorganosiloxane (A) containing alkenyl groups preferably conforms to the average general formula (1)
R1xR2ySiO(4-x-y)/2xe2x80x83xe2x80x83(1), 
in which
R1 is a monovalent, optionally halogen- or cyano-substituted C1-C10-hydrocarbon radical containing aliphatic carbonxe2x80x94carbon multiple bonds which is optionally bonded to silicon via a divalent organic group,
R2 is a monovalent, optionally halogen- or cyano-substituted C1-C10-hydrocarbon radical containing no aliphatic carbonxe2x80x94carbon multiple bonds which is bonded via SiC,
x is a non-negative number such that at least two radicals R1 are present in each molecule, and
y is a non-negative number such that (x+y) is in the range from 1.8 to 2.5.
The alkenyl groups R1 are able to undergo an addition reaction with an SiH-functional crosslinking agent. Use is usually made of alkenyl groups having from 2 to 6 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl, 5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl or cyclohexenyl groups, preferably vinyl or allyl groups. The radicals R1 can be bonded in any position of the polymer chain, in particular to the terminal silicon atoms.
Divalent organic groups via which the alkenyl groups R1 can be bonded to silicon in the polymer chain consist, for example, of oxyalkylene units, such as, but not limited to, those of the general formula (2)
xe2x80x94(O)m[(CH2)nO]oxe2x80x94xe2x80x83xe2x80x83(2), 
in which
m has a value of 0 or 1, in particular 0,
n has a value of 1 to 4 in particular 1 or 2, and
o has a value of from 1 to 20, in particular from 1 to 5, including oxyalkylene moieties where the repeating methylene groups bear lower alkyl substituents. The oxyalkylene units of the general formula (2) are bonded on the left to a silicon atom.
Examples of unsubstituted radicals R2 are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl or tert-pentyl radicals, hexyl radicals such as the n-hexyl radical, heptyl radicals such as the n-heptyl radical, octyl radicals such as the n-octyl radical and isooctyl radicals such as the 2,2,4-trimethylpentyl radical, nonyl radicals such as the n-nonyl radical, or decyl radicals such as the n-decyl radical; alkenyl radicals such as the vinyl, allyl, n-5-hexenyl, 4-vinylcyclohexyl and 3-norbornenyl radicals; cycloalkyl radicals such as cyclopentyl, cyclohexyl, 4-ethylcyclohexyl and cycloheptyl radicals, norbornyl radicals and methylcyclohexyl radicals; aryl radicals such as the phenyl, biphenylyl and naphthyl radicals; alkaryl radicals such as o-, m- and p-tolyl radicals and ethylphenyl radicals; and aralkyl radicals such as the benzyl radical, and the alpha- and xcex2-phenylethyl radicals.
Examples of substituted hydrocarbon radicals R2 are halogenated hydrocarbons, such as the chloromethyl, 3-chloropropyl, 3-bromopropyl, 3,3,3-tri-fluoropropyl and 5,5,5,4,4,3,3-hexafluoropentyl radicals and the chlorophenyl, dichlorophenyl and trifluorotolyl radicals.
R2 preferably has from 1 to 6 carbon atoms. Particular preference, is given to methyl and phenyl.
Constituent (A) may also be a mixture of polyorganosiloxanes which contain various alkenyl groups and which differ, for example, in the alkenyl group content, the nature of the alkenyl group or structurally. While it is possible for some of the molecules of constituent (A) to contain less than 2 unsaturated groups, on average, at least two of such groups should be present per molecule.
The structure of the polyorganosiloxanes (A) containing alkenyl groups can be linear, cyclic, or branched. The content of tri- and/or tetrafunctional units resulting in branched polyorganosiloxanes is typically very low, preferably at most 20 mol %, and in particular at most 0.1 mol %.
Particular preference is given to the use of polydimethylsiloxanes containing vinyl groups whose molecules conform to the general formula (3)
(ViMe2SiO1/2)2(ViMeSiO)p(Me2SiO)qxe2x80x83xe2x80x83(3), 
where the non-negative integers p and q satisfy the following relations: pxe2x89xa70, 50 less than (p+q) less than 20,000, preferably 200 less than (p+q) less than 1000, and 0 less than (p+1)/(p+q) less than 0.2.
The viscosity of the polyorganosiloxane (A) at 25xc2x0 C. is preferably from 0.5 to 100,000 Pa.s, in particular from 1 to 2000 Pa.s. The silicone compositions preferably comprise from 30 to 80% by weight, more preferably from 35 to 75% by weight, of polyorganosiloxane (A), and preferably constitute neat compositions optionally containing organic solvents, but are preferably not in the form of aqueous dispersions.
Examples of the non-reinforcing filler (B) are mineral and/or organic fillers. Examples of non-reinforcing fillers (B) are quartz, for example as quartz flour, talc, diatomaceous earth, clays, chalk, lithopones, carbon blacks, graphite, metal oxides, metal carbonates, metal sulfates, metal salts of carboxylic acids, metal dusts, fibers, such as glass fibers and plastic fibers, and plastic powders. Preference is given to talc and quartz. The fillers (B) may also have been surface-modified, for example with silylating agents.
The non-reinforcing filler talc has the advantage over other inactive mineral fillers, for example, quartz, that non-abrasive, oil-resistant, crosslinkable silicone compositions can be generated. Quartz-containing silicone compositions have the disadvantage that, owing to the high abrasiveness of quartz flour, they can only be processed on machines and tools with specially hardened steel. Talc-containing, oil-resistant silicone compositions can be processed without problems on standard injection-molding machines and tools.
The mean particle size of the filler (B) is preferably from 0.5 to 100 xcexcm, in particular from 1 to 50 xcexcm. The specific surface area of the filler (B) is preferably  less than 70 m2/g, more preferably  less than 50 m2/g. The silicon compositions preferably comprise from 2 to 60% by weight, more preferably from 5 to 50% by weight, of filler (B).
The silicone compositions may comprise an organic peroxide (C1) as the crosslinking component (C). By means of the organic peroxide (C1), which serves as a source of free radicals, the silicone compositions are crosslinked by means of free radicals.
Examples of organic peroxides (C1) are acyl peroxides such as dibenzoyl peroxide, bis(4-chlorobenzoyl) peroxide, bis(2,4-dichlorobenzoyl) peroxide and bis(4-methylbenzoyl) peroxide; alkyl peroxides and aryl peroxides such as di-tert-butyl peroxide, 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, dicumyl peroxide and 1,3-bis(tert-butylperoxyisopropyl)benzene; perketals such as 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane; peresters such as diacetyl peroxydicarbonate, tert-butyl perbenzoate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxyisononanoate, dicyclohexyl peroxydicarbonate and 2,5-dimethylhexane 2,5-diperbenzoate, and tert-butyl xcex2-hydroxyethyl peroxide. It is also possible to employ a combination of organic peroxides (C1), such as bis-4-methylbenzoyl peroxide and a single compound or at least two of the compounds from the group consisting of benzoyl peroxide, dicumyl peroxide, 2,5-dimethylhexane-2,5-diperbenzoate and di-tert-butyl peroxide.
The silicone compositions preferably comprise from 0.05 to 10% by weight, in particular from 0.1 to 2% by weight, of organic peroxide (C1).
The organosilicon compound (C2) containing at least two SiH functions per molecule preferably has a composition of the average general formula (4)
HaR3bSiO(4-a-b)/2xe2x80x83xe2x80x83(4), 
in which
R3 is a monovalent, optionally halogen- or cyano-substituted C1-C18-hydrocarbon radical containing no aliphatic carbonxe2x80x94carbon multiple bonds, which is bonded via SiC, and
a and b are non-negative integers,
with the proviso that 0.5 less than (a+b) less than 3.0 and 0 less than a less than 2, and that at least two silicon-bonded hydrogen atoms are present on average per molecule.
Examples of R3 are the radicals indicated previously for R2. R3 preferably has from 1 to 6 carbon atoms. Particular preference is given to methyl and phenyl.
Preference is given to the use of an organosilicon compound (C2) containing three or more SiH bonds per molecule. On use of an organosilicon compound (C2) having only two SiH bonds per molecule, it is advisable to use a polyorganosiloxane (A) which has at least three alkenyl groups on average per molecule.
The hydrogen content of the organosilicon compound (C2), based exclusively on the hydrogen atoms bonded directly to silicon atoms, is preferably in the range from 0.002 to 1.7% by weight of hydrogen, preferably from 0.1 to 1.7% by weight of hydrogen.
The organosilicon compound (C2) preferably contains at least three and at most 600 silicon atoms per molecule. Preference is given to the use of an organosilicon compound (C2) which contains from 4 to 200 silicon atoms per molecule. The structure of the organosilicon compound (C2) can be linear, branched, cyclic or network-like.
Particularly preferred organosilicon compounds (C2) are linear polyorganosiloxanes of the general formula (5)
(HR42SiO1/2)c(R43SiO1/2)d(HR4SiO2/2)e(R42SiO2/2)fxe2x80x83xe2x80x83(5), 
where
R4 is as defined for R3, and
the non-negative integers c, d, e and f satisfy the following relations: (c+d)=2, (c+e) greater than 2,5 less than (e+f) less than 200 and 1 less than e/(e+f) less than 0.1.
The SiH-functional organosilicon compound (C2) is preferably present in the crosslinkable silicone composition in such an amount that the molar ratio of SiH groups to alkenyl groups is from 0.5 to 5, more preferably from 1.0 to 3.0.
The hydrosilylation catalyst (C2) employed can be any known catalysts which catalyze the hydrosilylation reactions that occur on crosslinking of addition-crosslinking silicone compositions. The hydrosilylation catalysts (C2) may be, for example, metals and metal compounds, in particular of metals such as rhodium, palladium, ruthenium and iridium, preferably platinum. Preference is given to the use of platinum and platinum compounds. Particular preference is given to platinum compounds which are soluble in polyorganosiloxanes. The soluble platinum compounds used can be, for example, the platinum/olefin complexes of the formulae (PtCl2.olefin)2 and H(PtCl3.olefin), preference in the latter compounds being given to the use of alkenes having from 2 to 8 carbon atoms such as ethylene, propylene, isomers of butene and octene, or cycloalkenes having from 5 to 7 carbon atoms such as cyclopentene, cyclohexene and cycloheptene. Further soluble platinum catalysts are the platinum/cyclopropane complex of the formula (PtCl2C3H6)2, products of the reaction of hexachloroplatinic acid with alcohols, ethers and aldehydes or mixtures thereof, or the product of the reaction of hexachloroplatinic acid with methylvinylcyclotetrasiloxane in the presence of sodium bicarbonate in ethanolic solution. Particular preference is given to complexes of platinum with vinylsiloxane, such as sym-divinyltetramethyldisiloxane. The platinum compounds described in EP-A-1077226 and EP-A-994159 are likewise very suitable.
The hydrosilylation catalyst (C2) can be employed in any desired form, including, for example, in the form of microcapsules containing hydrosilylation catalyst, or organopolysiloxane particles, as described in EP-A-1006147. The content of hydrosilylation catalysts (C2) is preferably selected in such a way that the addition-crosslinkable silicone composition has a Pt content of 0.1-200 ppm, preferably 0.5-40 ppm, when platinum catalysts are employed.
The amino or ammonium compound (D) can have any desired structure. Suitable are, for example, amino compounds (D) of the general formula (6) and ammonium compounds (D) of the general formula (7)
NR5R6R7xe2x80x83xe2x80x83(6), 
[NR5R6R7R8]+Xxe2x88x92xe2x80x83xe2x80x83(7), 
in which
R5, R6, R7 and R8 are a hydrogen atom, a hydroxyl group, a monovalent, optionally halogen- or cyano-substituted C1-C25-hydrocarbon radical, in which non-adjacent methyl groups may have been replaced by xe2x80x94NR92 groups, methylene groups may have been replaced by xe2x80x94Oxe2x80x94 or xe2x80x94NR9xe2x80x94 groups and methylene groups may have been replaced by xe2x80x94Nxe2x95x90 groups, where 2 or 3 of the radicals R5, R6 and R7 together may form an aliphatic or aromatic ring or polycyclic structure,
R9 is a hydrogen atom, a hydroxyl group or a monovalent, optionally halogen- or cyano-substituted C1-C10-hydrocarbon radical, and
Xxe2x88x92 is selected from an OH, halogen, and acid anions.
The hydrocarbon radicals R5, R6, R7 and R8 preferably have at most 15 carbon atoms. The hydrocarbon radicals R9 are more preferably aliphatic, and most preferably have 6 carbon atoms or less.
Examples of nitrogen compounds (D) in which non-adjacent methyl groups in R5, R6, R7 and R8 have been replaced by xe2x80x94NR92 groups, methylene groups have been replaced by xe2x80x94NR9xe2x80x94 groups and methine groups have been replaced by xe2x80x94Nxe2x95x90 groups include CH3CH2CH2NHCH2CH2NH2 and CH3CH2xe2x80x94CH2N(CH2CH2NHCH3)2. Examples where 2 or 3 of the radicals R5, R6 and R7 together can form an aliphatic or aromatic ring or polycyclic structure are heterocyclic compounds such as morpholine, pyrimidine, pyridine and pyrrole, and derivatives thereof. Examples of acid anions X are CO32xe2x88x92 and CH3CH2COOxe2x88x92.
Nitrogen-containing organosilicon compounds (D) can be, for example, silanes, siloxanes and silazanes.
The nitrogen-containing silanes and siloxanes (D) preferably contain Sixe2x80x94C-bonded radicals of the general formula (8)
R5R6Nxe2x80x94R10xe2x80x94xe2x80x83xe2x80x83(8), 
in which
R5 and R6 are as defined above, and
R10 is a divalent C1-C15-hydrocarbon radical, in particular an alkylene radical, preferably an alkylene radical having from 1 to 6 carbon atoms.
The structure of the polyorganosiloxanes (D) can be linear, cyclic or branched.
Examples of silanes (D) are H2Nxe2x80x94(CH2)3xe2x80x94Si(OR)3 and H2Nxe2x80x94(CH)2xe2x80x94NHxe2x80x94(CH2)3xe2x80x94Si(OR)3.
Examples of siloxanes (D) are H2Nxe2x80x94(CH2)3xe2x80x94Si(CH3)2[xe2x80x94Oxe2x80x94Si(CH3)2]zxe2x80x94(CH2)3xe2x80x94NH2 and H2Nxe2x80x94(CH2)2xe2x80x94NHxe2x80x94(CH2)3xe2x80x94Si(CH3)2[xe2x80x94Oxe2x80x94Si(CH3)2]zxe2x80x94(CH2)3xe2x80x94NHxe2x80x94(CH2)2xe2x80x94NH2, where z can have values of from 1 to 1000. However, the amino groups may also be bonded in the middle or at the ends of the chains.
Examples of silazanes are hexamethyldisilazane and divinyltetramethyldisilazane, and derivatives thereof.
An example of an amido compound (D) is bis(trimethylsilyl)acetamide CH3C[xe2x95x90Nxe2x80x94Si(CH3)3]OSi(CH3)3 and derivatives thereof.
The nitrogen compounds (D) may optionally be those which liberate amino compounds during storage or during crosslinking or during subsequent heating of the crosslinked silicone elastomers.
Preference is given to low-volatility basic amino compounds having a boiling point above 100xc2x0 C., particularly preferably above 150xc2x0 C., preferably the aminoalkyl-functionalized siloxanes and silanes described above.
The N content introduced into the silicone compositions via the nitrogen compounds (D) is 10 to 10,000 ppm, preferably 15 to 1000 ppm, more preferably 15 to 500 ppm, in each case based on the sum of constituents (A) and (B).
The mechanical strength of the vulcanized silicone rubber is increased if the silicone compositions comprise actively reinforcing fillers as constituent (E). The actively reinforcing fillers (E) used are especially precipitated silicic acids and more preferably, pyrogenic silicic acids, and mixtures thereof. The specific surface area of these actively reinforcing fillers should be at least 50 m2/g, and/or preferably in the range from 200 to 400 m2/g, as determined by the BET method. Actively reinforcing fillers of this type are very well-known materials in the area of silicone rubbers. The content of actively reinforcing filler (E) in the addition-crosslinkable silicone compositions is preferably in the range from 5 to 60% by weight, more preferably from 10 to 40% by weight.
The crosslinkable silicone compositions may optionally comprise, as constituent (F), further additives in a proportion of up to 70% by weight, preferably from 0.0001 to 40% by weight. These additives can be, for example, resin-like polyorganosiloxanes which are different from the diorganopolysiloxanes (A) and (C2), dispersion aids, solvents, adhesion promoters, pigments, dyes, plasticizers, organic polymers, heat stabilizers, etc. These include additives such as dyes, pigments, etc. Furthermore, thixotropic constituents, such as highly disperse silicic acid or other commercially available thixotropic additives, may be present as constituent (F). In addition, siloxanes of the formula HSi(CH3)2xe2x80x94[Oxe2x80x94Si(CH3)2]wxe2x80x94H, where w has a value of from 1 to 1000, may also be present as chain extenders.
It is furthermore possible for additives (F) to be present, which serve to set the processing time, initiation temperature and crosslinking rate of the crosslinking compositions in a specific manner. These inhibitors and stabilizers are very well known in the area of crosslinking compositions. Additives which improve the compression set may also be added. In addition, hollow bodies, blowing agents for the production of foams, and/or non-vinyl-functionalized polydiorganosiloxanes may also be added.
The compounding of the crosslinkable silicone compositions is carried out by mixing the above-mentioned components in any desired sequence. The crosslinking of the crosslinkable silicone compositions is preferably carried out by warming, preferably at from 30 to 250xc2x0 C., preferably at at least 50xc2x0 C., more preferably at at least 100xc2x0 C., preferably at a maximum of 200xc2x0 C., more preferably at a maximum of 180xc2x0 C.
The invention also relates to the silicone elastomers which are obtainable by crosslinking the crosslinkable silicone compositions, and to the use of a nitrogen compound (D) selected from amino, ammonium and amido compounds and nitrogen-containing organosilicon compounds for improving the heat stability of elastomers obtained by crosslinking silicone compositions which comprise the constituents:
(A) from 20 to 99% by weight of a polyorganosiloxane containing at least two alkenyl groups per molecule and having a viscosity at 25xc2x0 C. of from 0.1 to 500,000 Pa.s,
(B) from 1 to 80% by weight of a non-reinforcing filler having a mean particle size of from 0.1 to 200 xcexcm and a specific surface area of  less than 100 m2/g,
(C) a crosslinking component selected from
(C1) an organic peroxide and
(C2) an organosilicon compound containing at least two SiH functions per molecule in combination with a hydrosilylation catalyst.
The definitions of all the above symbols in the above formulae are each independent of one another. In all formulae, the silicon atom is tetravalent.
In the following examples, unless stated otherwise, all amounts and percent data are based on the weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20xc2x0 C.